How to: Change Resolution on Ubuntu Desktop in a Oracle VM Virtual Box

In this guide, I will be showing you how you can update the resolution of your Ubuntu Virtual Machine using VirtualBox. Using these instructions should allow you to scale the desktop of your VM to your current resolution. Although this is not guaranteed to work, its a pretty good start to get you going.
https://youtu.be/NHVuXNTCABc

Prerequisites

In order to follow this tutorial, you will need the following

Ubuntu Virtual Machine using VirtualBox

Sudo privileges (or root access)

Installing Guest Additions

To get started with this, you will need to open up your virtual machine and login. When you are sitting at the desktop, you will need to go to the devices menu at the top and select 'Install Guest Additions CD Image...'.

After clicking this, you will get a warning message popup like this

You can ignore this and just click run. You will then be prompted to enter your password - You should go ahead and do this!

A Terminal window should now pop up and start the installation process. After a couple of minutes, you should see the prompt 'Press Return to close this window...'

The installation is now complete. You can go ahead and press the Return key and then do a full restart.

After restarting and logging in, you should notice that the desktop is larger and that you can in fact maximise the window to get a full screen desktop!

If for any reason this didnt work, please try the instructions mentioned here